1. Field of the Invention
This invention relates generally to strong, yet light weight articles, such as fastener elements and, more particularly, to composite fasteners. The invention also relates to methods of manufacturing such fasteners.
2. Description of the Prior Art
Many types of light weight fasteners have been developed and utilized for securing together certain highly stressed components, such as aircraft parts. For such applications the fasteners usually require high strength and light weight. Virtually all of the prior types of fasteners for such applications have had some advantages and several disadvantages.
One common type of prior light weight fastener includes those fabricated with a light weight metallic core material to which a different metallic material is applied as a thin protective coating. Such coating may be applied by plating, galvanizing, or other application method. In such fastener design, the reduction in weight normally results in a corresponding reduction in strength along with a corresponding reduction in the ability of the fastener to withstand one or more of the stresses to which it may be subjected.
Another common type of prior light weight fastener includes those with a molded, non-metallic core material coated with a layer of metal. Such design provides for light weight fasteners without a significant increase in size. Such fasteners, however, typically have limited strength and are unlikely to withstand severe stress and tension forces. Also, during use of such fasteners in metallic structures, the relatively thin metallic coating is often quickly abraded or otherwise destroyed permitting components secured by the fastener to act against the more fragile core material. Thus, under high stress conditions failures may occur by the cutting or shearing of the core.
Illustrative of another prior approach to light weight fasteners is that disclosed in U.S. Pat. No. 3,495,494 to Scott. This patent discloses the fabrication of a hollow threaded fastener of resin impregnated glass fiber filaments. A cylinder of parallel filaments is first formed about an interior mold. The fibers and resin of the cylinder are then forced against an external mold by means of a pressurized fluid which may be injected into the interior. This pressurized fluid does not become part of the fastener. Alternatively, the bundle of fibers may be compressed by applying a force through movable sections of an external mold, or the bundle of fibers may be compressed internally against the mold by means of an inflatable central mandrel.
Another example of fabricating light weight fasteners of resin material reinforced by parallel threads or fibers of material, such as glass, is shown in U.S. Pat. No. 3,382,050 to Boggs. In accordance with that disclosure, a unidirectional cylinder of fibers is placed in the mold at one end and liquid resin material is fed into a passage maintained at either cool or warmer temperatures by means of the circulation of a temperature modifying medium within the hollow jackets. The fiber cylinder and the resin are continuously fed into the upper end of the mold and a cured threaded fastener rod is continuously removed from the lower end of the mold. The removed material is subsequently cut to length. The resulting fastener is thus formed of a resin compound reinforced with axially oriented fibrous material with a hollow interior. While suitable for a number of applications, this fastener structure, like the Scott fastener, does not appear to be sufficiently strong to withstand the tension forces typically encountered in an airframe environment without sever size penalties.
A fastener structure of plastic molded around a metal core is shown in U.S. Pat. No. 4,351,786 to Mueller. The metal core is not threaded and does not extend to the ends of the molded plastic structure. Further, neither the metal core nor the molded plastic structure contain fiber reinforcements.
As illustrated by the number of prior patents, efforts are continuously being made in an attempt to solve the problem of economically fabricating strong, yet light weight articles. None of these patents, however, discloses or suggests the present inventive combination of elements and method steps for reliably, conveniently and economically fabricating strong yet light weight composite fasteners of reinforced resin material as disclosed herein. The present invention achieves its purposes, objectives, and advantages over the prior art through new, useful, and unobvious elements and method steps, with a minimum number of parts, at a reduction of cost in terms of both materials and labor, and through the utilization of readily available materials.
These purposes, objects, and advantages should be construed as merely illustrative of some of the more prominent features and applications of the present invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other purposes, objects, and advantages as well as a fuller understanding of the invention may be had by referring to the summary of the invention and detailed description describing the preferred embodiments of the invention in addition to the scope of the invention as defined by the claims taken in conjunction with the accompanying drawings.